1. Technical Field
The invention relates to a clamping and/or spreading tool, comprising a push or pull rod to which a movable jaw is fixed, a stationary jaw, a gear mechanism by which the movable jaw is movable towards or away from the stationary jaw by displacement of the push or pull rod in a clamping or spreading direction and by which clamping and/or spreading forces are applicable between the jaws, further comprising a lock which blocks displacement of the push or pull rod in opening direction opposite to the clamping or spreading direction so as to maintain the clamping and/or spreading forces generated between the jaws.
2. Background Art
DE 103 35 365 A1 discloses a clamping or spreading tool of this kind which can generate very great clamping forces between the stationary and movable jaws. To accomplish that, the pivot arm is pivotably mounted at a clamping side of the push or pull rod on a support which holds the stationary jaw. The point of contact at which the actuating arm can introduce actuating forces into an entraining slide element of the gear mechanism likewise is provided at the clamping side of the push or pull rod between the swivel joint and the push or pull rod. The leverage thus achieved is apt to provide clamping or spreading forces of up to 3000 Newton between the clamping jaws when the clamping tool is manipulated by one hand.
Once great tensioning forces have been generated, it may happen that actuation for release of the draw-back lock retaining the high tension will cause the movable jaw to be propelled explosively away from the stationary jaw. Analyses have clearly demonstrated that the clamping tool, especially the material of the clamping jaws, when tensioned, behaves like an elastic system deforming elastically in accordance with the tension created. Discharging of the clamping tool unloads the stored tension in correspondence with the modulus of elasticity inherent in the system by a shock-like movement of the push or pull rod in opening direction. The stored potential tensional energy is converted into kinetic energy of the push or pull rod. And it may happen that the push or pull rod is launched right through the support of the stationary jaw.
Since it is preferred to keep a low friction profile of the push rod within the support to permit easy displacement and adjustment of the push or pull rod, the release of very great tensional forces may let the push or pull rod, together with the movable jaw, glide through the support without any deceleration, whereby not only the workpiece to be treated may be damaged but also the person handling the tool may be hurt.